Congrats, the "Mesentery" Brings Your Organ Total to 79

In 2016, the grand total of organs in a human body was a round, respectable 78. Not so in 2017; a lot can change in a year. Today, if a medical professional were to inventory your internal goods, the final count would be an unwieldy, puzzling 79.

No, humans didn’t grow another organ in the span of 365 days. Rather, scientists finally reassessed some long-held assumptions about our bodies — particularly how our intestines are held to the walls of the abdomen. For centuries, anatomists believed they were connected via an inconsequential, fragmented series of tissues, but, as scientists report in The Lancet: Gastroenterology and Hepatology, they’re anchored by the mesentery, a fold of tissue that is finally being recognized as what it truly is: an organ.

Turns out the mesentery is one continuous organ.

It isn’t easy to get into the organ club: Scientists withhold that status for those parts of the body that are not only self-contained but also provide some vital function to the body. Because research on the mesentery over the past 100 years suggested that it was made up of several pieces rather than one, continuous band of tissue locking the intestines in place, it was mostly disregarded. Connective tissue is plentiful in the human body, after all.

But when scientists from the University Hospital Limerick in Ireland took a closer look, they realized it was actually a continuous structure. It’s made up of a doubl folded swath of peritoneum, which lines the bag of guts we call the abdominal cavity. In this regard, it met both of the requirements for “organ” status: It’s a discrete structure with the undeniably important function of holding our digestive system in place.

While it may seem like the mesentery’s reclassification may do nothing but make life more difficult for budding anatomists, the researchers behind the study hope that the new discovery might change the way scientists think about diseases in the digestive system. With the mesentery now on physicians’ radars, it’ll be considered the way the rest of the abdominal organs are — as a potential player in the rise of human disease.